LLVM Weekly - #255, November 19th 2018
Welcome to the two hundred and fifty-fifth issue of LLVM Weekly, a weekly newsletter (published every Monday) covering developments in LLVM, Clang, and related projects. LLVM Weekly is brought to you by Alex Bradbury. Subscribe to future issues at https://llvmweekly.org and pass it on to anyone else you think may be interested. Please send any tips or feedback to asb@asbradbury.org, or @llvmweekly or @asbradbury on Twitter.
News and articles from around the web
Videos from the 2018 LLVM Developers' Meeting are starting to be posted on the LLVM Foundation's YouTube channel.
Reminder: the deadline for the LLVM Toolchain Devroom at FOSDEM CfP is this coming Sunday 25th November.
Robert O'Callahan has written a blog post which compares the quality of debug information produced by Clang and GCC.
On the mailing lists
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JF Bastien has started an RFC thread on automatic variable initialisation in Clang. The proposed patch allows automatic variables to be initialized with either a pattern or with zeroes. There are some concerns that zero-initialisation might be over-relied upon, effectively creating a new dialect of C++. Kostya Serebryany shares a long list of bugs, vulnerabilities, and exploits based on uses of uninitialized memory.
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Yitzhak Mandelbaum is proposing a framework that makes it easier to write source-to-source transformations with the clang::Tooling libraries, and is seeking comments.
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Kristina Brooks is wondering if there is any interest in a
_Manglecompiler extension for converting strings to identifiers/symbols. -
Sam McCall is seeking feedback on using the VirtualFileSystem abstraction for real filesystem interaction.
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John Brawn is looking for feedback on how to improve SimplifyCFG block speculation. Krzysztof Parzyszek is in favour of rewriting SimplifyCFG.
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Erich Keane would like to know if anyone has any concerns about removing support for pre-tokenized headers from Clang.
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Matthew Davis kicked off an RFC discussion on adding binary support to llvm-mca, allowing selected regions of code in an object file to be analysed.
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Sjoerd Meijer proposes that
-Ozshould imply-mthumb. Some respondents are concerned that changing the the target instruction set based on optimisation level may be confusing.
LLVM commits
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A new
fnegIR instruction was introduced. r346774. -
The MSP430 backend now has an MC layer implementation. r346948, r346949.
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Initial 'scaffolding' for a GN build system was added. As explained in the commit message, this build is unsupported. So far, just enough build logic was added to build llvm/lib/Demangle. r347128.
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An OptimizerLast extension point was added to th new pass manager. r346645.
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FileCheck learned a new CHECK-COUNT-num directive which matches the same pattern exactly
numtimes. r346722. -
The WebAssembly backend gained support for the event section as specified in the WebAssembly exception handling proposal. r346825.
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A new superword-level parallelism analysis has been implemented on top of VPlan. r346857.
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The MachineScheduler will now bias physical register immediate assignments to minimize live ranges. r346894.
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The RISC-V backend gained a new helper for immediate materialisation. r346937.
Clang commits
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The Clang AST APIs were updated to allow limiting the scope of common AST traversals. r346847.
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llvm-config has been deprecated as a method for detecting an LLVMinstallation. r346732.
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The Clang CMake build-system was enhanced to support cross-compiling with multi-stage builds. r347025.